When my 69 Riviera engine is idling I can hear a vacuum leak from under the hood. If I depress the brake pedal a tad it goes away. I found the leak, it is from a hole under the master cylinder. See pictures attached. I guess something has gone missing. Anybody know what part should be there? Regards, Kenneth
Nothing should be in that hole. That hole is part of the master cylinder casting. Are you absolutely sure the leak is from there? I guess its plausible that the casting could be porous, but IMO unlikely. Would be easy to determine- does the noise goes away when you cover it with your thumb and forefinger? Is there an increase in vacuum on a vacuum gauge when you do it? What vacuum reading do you get at idle vs piching off the line to the booster?
See http://www.v8buick.com/showthread.php?247470-Vaccum-leak-from-master-cylinder . The hole you found is there by design, but if air is moving through it with the engine running it's due to a booster leak. Devon
Funny, I never noticed the vent hole inside that loop in the casting. Thanks for the explanation in the other thread Devon. I learned something
The vent hole by design serves two functions: 1. It allows you to identify a failure of the master cylinder as a fluid leak and a booster failure as a vacuum leak. 2. If you have a failure, it prevents the booster from sucking fluid out of the master cylinder and exacerbating the problem,.without the vent hole, you would have no indication of failure until you lost fluid and braking. A kind of safety factor.
Jason, I covered the holes with my fingers and it stopped the leak so I know for sure that is where the leak is. Devon, thanks for the link! That explains it all
